a(n) = Sum_{d|n} mu(n/d) * binomial(d,4).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =5a(5) =15a(6) =35a(7) =69a(8) =126a(9) =205a(10) =330a(11) =479a(12) =715a(13) =966a(14) =1360a(15) =1750a(16) =2380a(17) =2919a(18) =3876a(19) =4634a(20) =5950a(21) =6985a(22) =8855a(23) =10062a(24) =12645a(25) =14235a(26) =17424a(27) =19473a(28) =23751a(29) =25820